Touch sensing device and display apparatus including the same

ABSTRACT

Disclosed is a touch sensing device for preventing touch sensing performance from being reduced by a parasitic capacitance. The touch sensing device includes a plurality of buffers buffering a difference between a reference signal and a reception signal received from a touch electrode and generating first and second currents corresponding to a buffered signal, a plurality of current mirror units generating a first output signal using a first mirror current generated through mirroring of the first current and a third mirror current generated through mirroring of the second current and generate a second output signal using a second mirror current generated through mirroring of the first current and a fourth mirror current generated through mirroring of the second current, and a plurality of integrators integrating a difference between the first output signal from an nth current mirror unit and the second output signal from an (n−1)th current mirror unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the Korean Patent Application No.10-2018-0170722, filed on Dec. 27, 2018, which is hereby incorporated byreference as if fully set forth herein.

FIELD

The present disclosure relates to a touch sensing device, and moreparticularly, to a touch sensing device for sensing a touch applied to adisplay panel.

BACKGROUND

With the advancement of information-oriented society, variousrequirements for display apparatuses for displaying an image areincreasing. Recently, various types of display apparatuses such asLiquid Crystal Display (LCD) and Organic Light Emitting Diode (OLED)display are being practically used.

Recently, display apparatuses including a touch screen panel for sensinga touch input based on a stylus pen or a finger of a user are beingwidely used without depending on conventional input manners such asbuttons, keyboards, and mouse devices. The display apparatuses includingthe touch screen panel include a touch sensing device for accuratelydetecting the presence of a touch and touch coordinates (a touchposition).

The touch sensing device drives touch electrodes disposed in the touchscreen panel to detect a touch sensing signal and detects touchinformation such as the presence of a touch or a touch position by usingthe touch sensing signal.

In a related art touch sensing device, an undesired parasiticcapacitance may occur between touch driving patterns and peripheralconductors at the inside or outside of a touch screen in a process ofdriving the touch screen to sense a touch. When a touch is sensed as acapacitive type in a state where a parasitic capacitance occurs insideor outside the touch screen panel, touch sensitivity may be greatlyreduced due to the parasitic capacitance. Such a problem may moreseverely occur in a case where the touch screen panel is embedded into adisplay panel.

Particularly, in plastic organic light emitting diode (pOLED) displaysof which the use is increasing in smartphones and the like, as athickness of each smartphone is progressively thinned, a high parasiticcapacitance occurs between a touch screen panel and a cathode electrodeof a plastic OLED. Due to the high parasitic capacitance, it isdifficult to design a sensing amplifier based on a feedback factor of atouch sensing device for sensing a touch.

Moreover, since a feedback capacitor applied to a sensing amplifier of atouch sensing device should increase due to an increase in a parasiticcapacitance, a design area of the touch sensing device increases, andmoreover, an output signal of the sensing amplifier is reduced.

In addition, display noise may penetrate into a touch screen panel dueto a parasitic capacitance, causing the degradation in signal noiseratio (SNR) characteristic.

SUMMARY

Accordingly, the present disclosure is directed to providing a touchsensing device and a display apparatus including the same thatsubstantially obviate one or more problems due to limitations anddisadvantages of the related art.

An aspect of the present disclosure is directed to providing a touchsensing device and a display apparatus including the same, which preventtouch sensing performance from being reduced by a parasitic capacitance.

Additional advantages and features of the disclosure will be set forthin part in the description which follows and in part will becomeapparent to those having ordinary skill in the art upon examination ofthe following or may be learned from practice of the disclosure. Theobjectives and other advantages of the disclosure may be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the disclosure, as embodied and broadly described herein, there isprovided a touch sensing device including: a plurality of buffersbuffering a difference between a reference signal and a reception signalreceived from a touch electrode through a touch sensing line andgenerating first and second currents corresponding to a buffered signal;a plurality of current mirror units respectively connected to theplurality of buffers to generate a first output signal using a firstmirror current generated through mirroring of the first current and athird mirror current generated through mirroring of the second currentand generate a second output signal using a second mirror currentgenerated through mirroring of the first current and a fourth mirrorcurrent generated through mirroring of the second current; and aplurality of integrators integrating a difference between the firstoutput signal output from an n^(th) (where n is an integer of 2 or more)current mirror unit of the plurality of current mirror units and thesecond output signal output from an (n−1)th current mirror unit of theplurality of current mirror units.

In another aspect of the present disclosure, there is provided a touchsensing device including a first buffer connected to a first touchelectrode through a first touch sensing line, the first buffer includinga first output circuit including a first pull-up circuit having acascode configuration and a first pull-down circuit having a cascodeconfiguration; a first PMOS cascode mirror current generating circuitconnected to the first buffer to generate a first mirror current byperforming a mirroring operation on a first current flowing through thefirst pull-up circuit; a first NMOS cascode mirror current generatingcircuit connected to the first buffer to generate a third mirror currentby performing a mirroring operation on a second current flowing throughthe first pull-down circuit; and an integrator integrating a differencebetween a predetermined reference signal and a first output signalgenerated by using the first mirror current and the third mirrorcurrent.

In another aspect of the present disclosure, there is provided a displayapparatus including: a touch screen panel including a plurality of touchelectrodes and a plurality of touch sensing lines connected to theplurality of touch electrodes to each transmit a reception signalcorresponding to a capacitance generated in a corresponding touchelectrode; and a touch sensing device connected to the plurality oftouch sensing lines to sense whether a touch is applied thereto, whereinthe touch sensing device comprises: a first buffer connected to a firsttouch electrode through a first touch sensing line, the first bufferincluding a first output circuit including a first pull-up circuithaving a cascode configuration and a first pull-down circuit having acascode configuration; a first PMOS cascode mirror current generatingcircuit connected to the first buffer to generate a first mirror currentby performing a mirroring operation on a first current flowing throughthe first pull-up circuit; a first NMOS cascode mirror currentgenerating circuit connected to the first buffer to generate a thirdmirror current by performing a mirroring operation on a second currentflowing through the first pull-down circuit; and an integratorintegrating a difference between a predetermined reference signal and afirst output signal generated by using the first mirror current and thethird mirror current.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiments of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a block diagram of a display apparatus including a touchsensing device according to an embodiment of the present invention;

FIG. 2 is a circuit diagram for describing an operation of the touchsensing device illustrated in FIG. 1;

FIG. 3 is a circuit diagram illustrating a buffer and a current mirrorunit each illustrated in FIGS. 1 and 2;

FIG. 4 is a circuit diagram for describing self-capacitance sensing byusing a touch sensing device according to an embodiment of the presentinvention; and

FIG. 5 is a block diagram of a display apparatus including a touchsensing device and an I/Q demodulator according to another embodiment ofthe present invention.

DETAILED DESCRIPTION

In the specification, it should be noted that like reference numeralsalready used to denote like elements in other drawings are used forelements wherever possible. In the following description, when afunction and a configuration known to those skilled in the art areirrelevant to the essential configuration of the present disclosure,their detailed descriptions will be omitted. The terms described in thespecification should be understood as follows.

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following embodimentsdescribed with reference to the accompanying drawings. The presentdisclosure may, however, be embodied in different forms and should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present disclosureto those skilled in the art. Further, the present disclosure is onlydefined by scopes of claims.

A shape, a size, a ratio, an angle, and a number disclosed in thedrawings for describing embodiments of the present disclosure are merelyan example, and thus, the present disclosure is not limited to theillustrated details. Like reference numerals refer to like elementsthroughout. In the following description, when the detailed descriptionof the relevant known function or configuration is determined tounnecessarily obscure the important point of the present disclosure, thedetailed description will be omitted.

In a case where ‘comprise’, ‘have’, and ‘include’ described in thepresent specification are used, another part may be added unless ‘only˜’is used. The terms of a singular form may include plural forms unlessreferred to the contrary.

In construing an element, the element is construed as including an errorrange although there is no explicit description.

In describing a position relationship, for example, when a positionrelation between two parts is described as ‘on˜’, ‘over˜’, ‘under˜’ and‘next˜’ one or more other parts may be disposed between the two partsunless ‘just’ or ‘direct’ is used.

In describing a time relationship, for example, when the temporal orderis described as ‘after˜’, ‘subsequent˜’, ‘next˜’, and ‘before˜’, a casewhich is not continuous may be included unless ‘just’ or ‘direct’ isused.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure.

An X axis direction, a Y axis direction, and a Z axis direction shouldnot be construed as only a geometric relationship where a relationshiptherebetween is vertical, and may denote having a broader directionalitywithin a scope where elements of the present disclosure operatefunctionally.

The term “at least one” should be understood as including any and allcombinations of one or more of the associated listed items. For example,the meaning of “at least one of a first item, a second item, and a thirditem” denotes the combination of all items proposed from two or more ofthe first item, the second item, and the third item as well as the firstitem, the second item, or the third item.

Features of various embodiments of the present disclosure may bepartially or overall coupled to or combined with each other, and may bevariously inter-operated with each other and driven technically as thoseskilled in the art can sufficiently understand. The embodiments of thepresent disclosure may be carried out independently from each other, ormay be carried out together in co-dependent relationship.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a display apparatus including a touchsensing device according to an embodiment of the present invention.Referring to FIG. 1, the display device 100A may include a touch screenpanel (TSP) 103 and a touch sensing device 110A. The touch sensingdevice 110A may be packaged as a semiconductor package.

The display device 100A may be a mobile device, and the mobile devicemay be implemented as a laptop computer, a smartphone, a Mobile Internetdevice (MID), or an Internet of things (IoT) device. In an embodiment,the display device 100A may be a display apparatus including a plasticorganic light emitting diode (pOLED) display panel.

The touch screen panel 103 may include a plurality of touch drivinglines TX1 to TXm (where m is an integer of 2 or more) through which atouch driving signal is transmitted, a plurality of touch electrodes107, and a plurality of touch sensing lines 105-1 to 105-n (where n isan integer of 2 or more) through which voltages (or electric charges) ofthe touch electrodes 107 are transmitted. Each of the touch electrodes107 may include a mutual capacitor. The touch sensing lines 105-1 to105-n may denote sensing lines of the touch screen panel 103. In anembodiment, the touch screen panel 103 may be implemented as a typewhich is embedded into the display device 100A. For example, the touchscreen panel 103 may be disposed as an on-cell type in the displaydevice 100A.

In FIG. 1, the touch screen panel 103 is illustrated as amutual-capacitive touch screen panel including the touch driving linesTX1 to TXm and the touch sensing lines 105-1 to 105-n. However, thepresent invention is not limited thereto and may be applied to aself-capacitive touch screen panel where the supply of the touch drivingsignal and reception of a capacitance generated based on a user touch ora touch of a stylus pen are performed through one touch sensing line.

The touch sensing device 110A senses a touch applied to the touch screenpanel 103. In an embodiment, the touch sensing device 110A may supplythe touch driving signal to the touch electrodes 107 to drive the touchelectrodes 107 and may sense a variation of a capacitance caused by atouch applied to each of the touch electrodes 107. To this end, thetouch sensing device 110A may further include a touch driving signalsupply unit (not shown) which supplies the touch driving signal to thetouch electrodes 107 through the touch driving lines TX1 to TXm.

The touch sensing device 110A may include a plurality of buffers 120-1to 120-n connected to the touch sensing lines 105-1 to 105-n, aplurality of current mirror units 130-1 to 130-n, and a plurality ofintegrators 140-1 to 140-(n+1). In the drawings, a reference signillustrated as a small circle may denote an inverting terminal.

The plurality of buffers 120-1 to 120-n buffer a difference between areference signal REF and each of reception signals RX1 to RXnrespectively received through the touch sensing lines 105-1 to 105-n andoutput buffered signals BF1 to BFn. Output terminals, outputting outputsignals OUT1 to OUTn, of the buffers 120-1 to 120-n are respectivelyconnected to input terminals, receiving the reception signals RX1 toRXn, of the buffers 120-1 to 120-n.

In an embodiment, each of the buffers 120-1 to 120-n may be implementedas an operational amplifier having a voltage gain of 1. In this case,each of buffers 120-1 to 120-n of a first stage may be a unit gainbuffer, a unit gain amplifier, or a buffer amplifier.

According to an embodiment of the present invention, the touch sensinglines 105-1 to 105-n are respectively and directly connected to thebuffers 120-1 to 120-n, and thus, an additional circuit (for example, amultiplexer (MUX)) may not be needed between each of the buffers 120-1to 120-n and a corresponding touch sensing line of the touch sensinglines 105-1 to 105-n.

Moreover, according to an embodiment of the present invention, since thetouch sensing lines 105-1 to 105-n are respectively and directlyconnected to the buffers 120-1 to 120-n, signals may be simultaneouslygenerated in all transmission channels. Here, each of the transmissionchannels may denote a circuit which includes a buffer, a current mirrorunit, and an integrator each needed for processing the reception signalsRX1 to RXn.

Therefore, comparing with a conventional time sequence manner where atouch sensing device sequentially senses transmission channels, asensing time of the touch sensing device 110A may not increase or may beconsiderably shortened, and moreover, the degradation in signal qualitycaused by a time sequence-based sensing time difference may not occur ormay be considerably reduced.

In a conventional method where one touch sensing line is connected totwo channels and differential sensing is performed, there may be aproblem where an amplitude of a sensing signal decreases by half.However, according to an embodiment of the present invention, since thetouch sensing lines 105-1 to 105-n are respectively and directlyconnected to the buffers 120-1 to 120-n, the amplitude of a sensingsignal may not be reduced, and thus, a sensing signal having a highsignal noise ratio (SNR) may be obtained.

Moreover, a first stage of each transmission channel may be configuredwith a plurality of buffers 120-1 to 120-n, thereby solving a problemwhere it is difficult to design an amplifier due to a limitation of afeedback factor caused by a high capacitance load (for example,difficulty caused by an amplification speed and current consumption) anda design area increases due to the use of a large feedback capacitor.

In addition, according to an embodiment of the present invention, thereference signal REF for single-ended conversion may be used in a firsttransmission channel and a last transmission channel, and thus,algorithm processing may be easily performed on the reception signalsRX1 to RXn. For example, the algorithm may determine a transmissionchannel, where noise or a touch does not occur, between the firsttransmission channel and the last transmission channel and mayselectively convert differential signals obtained on the determinedtransmission channel into a single-ended signal.

The plurality of current mirror units 130-1 to 130-n may convert outputsignals BF1 to BFn, provided from the buffers 120-1 to 120-n, intocurrents and may provide converted currents to the integrators 140-1 to140-n, respectively. In an embodiment, each of the current mirror units130-1 to 130-n may be a charge-to-current converter which converts aninput electric charge into an output current.

The first current mirror unit 130-1 may copy a current flowing in anoutput circuit of the first buffer 120-1 to generate a pair of (or two)mirror currents RX1L and RX1R, the second current mirror unit 130-2 maycopy a current flowing in an output circuit of the second buffer 120-2to generate a pair of (or two) mirror currents RX2L and RX2R, and then^(th) current mirror unit 130-n may copy a current flowing in an outputcircuit of the n^(th) buffer 120-n to generate a pair of (or two) mirrorcurrents RXnL and RXnR.

In this case, the amounts of the two mirror currents RX1L and RX1R maybe the same, the amounts of the two mirror currents RX2L and RX2R may bethe same, and the amounts of the two mirror currents RXnL and RXnR maybe the same.

The amount of each of the two mirror currents RX1L and RX1R may beadjusted by using first control signals, the amount of each of the twomirror currents RX2L and RX2R may be adjusted by using second controlsignals, and the amount of each of the two mirror currents RXnL and RXnRmay be adjusted by using n^(th) control signals.

The first integrator 140-1 integrates a difference between the referencesignal REF and the mirror current RX1L of the first current mirror unit130-1. Accordingly, an integral signal corresponding to a differenceREF-RX1 between the reference signal REF and a first reception signalRX1 may be output from the first integrator 140-1.

The second integrator 140-2 integrates a difference between the mirrorcurrent RX1R of the first current mirror unit 130-1 and the mirrorcurrent RX2L of the second current mirror unit 130-2. Accordingly, anintegral signal corresponding to a difference RX1-RX2 between the firstreception signal RX1 and a second reception signal RX2 may be outputfrom the second integrator 140-2.

The (n+1)th integrator 140-(n+1) may integrate a difference between amirror current RXnR of the n^(th) current mirror unit 130-n and thereference signal REF. Accordingly, an integral signal corresponding to adifference RXn-REF between a n^(th) reception signal RXn and thereference signal REF may be output from the (n+1)th integrator140-(n+1).

FIG. 2 is a circuit diagram for describing an operation of the touchsensing device illustrated in FIG. 1. In FIG. 2, for convenience ofdescription, a configuration associated with the generating andprocessing of a first reception signal RX1 in the touch sensing device110A illustrated in FIG. 1 will be mainly described.

When a first reception signal RX1 transmitted through a first pad PAD1connected to a first touch sensing line 105-1 and a pulse VDRVcorresponding to the reference signal REF are input to the first buffer120-1, the first buffer 120-1 may output a current i₁ corresponding to abuffered signal BF1 to the first current mirror unit 130-1.

Moreover, when a second reception signal RX2 transmitted through asecond pad PAD2 connected to a second touch sensing line 105-2 and thepulse VDRV corresponding to the reference signal REF are input to thesecond buffer 120-2, the second buffer 120-2 may output a current i₂corresponding to a buffered signal BF2 to the second current mirror unit130-2.

Here, C₁ and C₂ may denote a touch capacitance (or a touch capacitor)generated from a touch screen panel 103 touched by a finger of a user,C_(P) may denote a parasitic capacitance (or a parasitic capacitor) ofthe touch screen panel 103, and C_(F) may denote a feedback capacitor. Kwill be described below with reference to FIG. 3

In this case, the first current mirror unit 130-1 may output the mirrorcurrents RX1L and RX1R, and the amounts of the mirror currents RX1L andRX1R may be the same, and thus, each of the mirror currents RX1L andRX1R may be expressed as the following Equation (1).

$\begin{matrix}{{RX_{1L}} = {{RX}_{1R} = \frac{i_{1}}{K}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

The second current mirror unit 130-2 may output the mirror currents RX2Land RX2R, and the amounts of the mirror currents RX2L and RX2R may bethe same, and thus, each of the mirror currents RX2L and RX2R may beexpressed as the following Equation (2).

$\begin{matrix}{{RX}_{2L} = {{RX_{2R}} = \frac{i_{2}}{K}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

The second integrator 140-2 may integrate a difference between themirror current RX1R output from the first current mirror unit 130-1 andthe mirror current RX2L output from the second current mirror unit 130-2to provide output signal. The output signal may be a difference RX1-RX2between a first reception signal RX1 and a second reception signal RX2or a signal corresponding to the difference RX1-RX2.

Hereinafter, an operation of each of a buffer and a current mirror unitaccording to an embodiment of the present invention will be described indetail with reference to FIGS. 1 to 3. FIG. 3 is a circuit diagramillustrating a buffer and a current mirror unit each illustrated inFIGS. 1 and 2. In FIG. 3, for convenience of description, only the firstbuffer 120-1, the first current mirror unit 130-1, the second buffer120-2, and the second current mirror unit 130-2 are illustrated.

The first buffer 120-1 may include a first operational amplifier AMP1and a first output circuit 125-1, and in order to configure a unit gainbuffer, an output terminal ND1 of the first operational amplifier AMP1may be connected to an input terminal, receiving the first receptionsignal RX1, of the first operational amplifier AMP1.

The first output circuit 125-1 may include a first pull-up circuit PU1and a first pull-down circuit PD1. Each of the first pull-up circuit PU1and the first pull-down circuit PD1 may be implemented as a cascodeconfiguration.

The first pull-up circuit PU1 may include a plurality of PMOStransistors P1 and P2 serially connected between the output terminal ND1and a first power line (or a power node) through which a first power VDDis provided, and in a pull-up operation (or a current sourcingoperation), a first current 11 may flow to the output terminal ND1through the first pull-up circuit PU1.

The first pull-down circuit PD1 may include a plurality of NMOStransistors N1 and N2 serially connected between the output terminal ND1and a second power line through which a second power VSS is provided,and in a pull-down operation (or a current sinking operation), a secondcurrent 12 may flow to the second power line through the first pull-downcircuit PD1.

The first current mirror unit 130-1 may include a first current mirrorcircuit 210 and a second current mirror circuit 230. The first currentmirror circuit 210 may include a first mirror current generating circuit215 and a second mirror current generating circuit 220, and the secondcurrent mirror circuit 230 may include a third mirror current generatingcircuit 235 and a fourth mirror current generating circuit 240.

The first current mirror circuit 210 may be implemented as a PMOScascode current mirror circuit and may perform a mirroring operation onthe first current 11 to generate a first mirror current MI1 and a secondmirror current MI2. Each of the first mirror current generating circuit215 and the second mirror current generating circuit 220 may beimplemented as a PMOS cascode current mirror circuit.

The first mirror current generating circuit 215 may include a pluralityof PMOS transistors P3 and P4 serially connected between a first mirroroutput terminal ND2 and the first power line through which the firstpower VDD is provided, and in a pull-up operation (or a current sourcingoperation), the first mirror current MI1 may flow to the first mirroroutput terminal ND2 through the first mirror current generating circuit215.

The second mirror current generating circuit 220 may include a pluralityof PMOS transistors P5 and P6 serially connected between a second mirroroutput terminal ND3 and the first power line through which the firstpower VDD is provided, and in a pull-up operation (or a current sourcingoperation), the second mirror current MI2 may flow to the second mirroroutput terminal ND3 through the second mirror current generating circuit220.

The first pull-up circuit PU1 and the first mirror current generatingcircuit 215 may configure a current mirror, and the first pull-upcircuit PU1 and the second mirror current generating circuit 220 mayconfigure a current mirror.

The amount of the first current 11 may be higher than the amount of eachof the first and second mirror currents MI1 and MI2, and the amount ofthe first mirror current MI1 may be the same as the amount of the secondmirror current MI2.

For example, when it is assumed that lengths of channels of the PMOStransistors P1 to P6 are the same, widths of the channels of the PMOStransistors P1 and P2 are the same, widths of the channels of the PMOStransistors P3 to P6 are the same, and the width of the channel of thePMOS transistor P1 is K (where K is an integer of 2 or more) times thewidth of the channel of the PMOS transistor P3, the amount of each ofthe first and second mirror currents MI1 and MI2 may be 1/K times theamount of the first current 11.

Under such an assumption, when widths of the channels of the PMOStransistors P3 to P6 are capable of being adjusted by using controlsignals, the amount of each of the first and second mirror currents MI1and MI2 may be adjusted.

The second current mirror circuit 230 may be implemented as an NMOScascode current mirror circuit and may perform a mirroring operation onthe second current 12 to generate a third mirror current MI3 and afourth mirror current MI4. Each of the third mirror current generatingcircuit 235 and the fourth mirror current generating circuit 240 may beimplemented as an NMOS cascode current mirror circuit.

The third mirror current generating circuit 235 may include a pluralityof NMOS transistors N3 and N4 serially connected between the firstmirror output terminal ND2 and the second power line through which thesecond power VSS, and in a pull-down operation (or a current sinkingoperation), the third mirror current MI3 may flow to the second powerline through the third mirror current generating circuit 235.Accordingly, a first output signal RX1L corresponding to a differencebetween the first mirror current MI1 and the third mirror current MI3may be output through the first mirror output terminal ND2.

The fourth mirror current generating circuit 240 may include a pluralityof NMOS transistors N5 and N6 serially connected between the secondmirror output terminal ND3 and the second power line through which thesecond power VSS, and in a pull-down operation (or a current sinkingoperation), the fourth mirror current MI4 may flow to the second powerline through the fourth mirror current generating circuit 240.Accordingly, a second output signal RX1R corresponding to a differencebetween the second mirror current MI2 and the fourth mirror current MI4may be output through the second mirror output terminal ND3.

The first pull-down circuit PD1 and the third mirror current generatingcircuit 235 may configure a current mirror, and the first pull-downcircuit PD1 and the fourth mirror current generating circuit 240 mayconfigure a current mirror.

The amount of the second current 12 may be higher than the amount ofeach of the third and fourth mirror currents MI3 and MI4, and the amountof the third mirror current MI3 may be the same as the amount of thefourth mirror current MI4.

For example, when it is assumed that lengths of channels of the NMOStransistors N1 to N6 are the same, widths of the channels of the NMOStransistors N1 and N2 are the same, widths of the channels of the NMOStransistors N3 to N6 are the same, and the width of the channel of theNMOS transistor N1 is K times the width of the channel of the NMOStransistor N3, the amount of each of the third and fourth mirrorcurrents MI3 and MI4 may be 1/K times the amount of the second current12.

Under such an assumption, when widths of the channels of the NMOStransistors N3 to N6 are capable of being adjusted by using controlsignals, the amount of each of the third and fourth mirror currents MI3and MI4 may be adjusted.

The second buffer 120-2 may include a second operational amplifier AMP2and a second output circuit 125-2, and in order to configure a unit gainbuffer, an output terminal ND4 of the second operational amplifier AMP2may be connected to an input terminal, receiving the second receptionsignal RX2, of the second operational amplifier AMP2.

The second output circuit 125-2 may include a second pull-up circuit PU2and a second pull-down circuit PD2. Each of the second pull-up circuitPU2 and the second pull-down circuit PD2 may be implemented as a cascodeconfiguration.

The second pull-up circuit PU2 may include a plurality of PMOStransistors P11 and P12 serially connected between the output terminalND4 and the first power line through which the first power VDD isprovided, and in a pull-up operation (or a current sourcing operation),a third current 13 may flow to the output terminal ND4 through thesecond pull-up circuit PU2.

The second pull-down circuit PD2 may include a plurality of NMOStransistors N11 and N12 serially connected between the output terminalND4 and the second power line through which the second power VSS isprovided, and in a pull-down operation (or a current sinking operation),a fourth current 14 may flow to the second power line through the secondpull-down circuit PD2.

The second current mirror unit 130-2 may include a third current mirrorcircuit 250 and a fourth current mirror circuit 270. The third currentmirror circuit 250 may include a fifth mirror current generating circuit255 and a sixth mirror current generating circuit 260, and the fourthcurrent mirror circuit 270 may include a seventh mirror currentgenerating circuit 275 and an eighth mirror current generating circuit280.

The third current mirror circuit 250 may be implemented as a PMOScascode current mirror circuit and may perform a mirroring operation onthe third current 13 to generate a fifth mirror current MI5 and a sixthmirror current MI6. Each of the fifth mirror current generating circuit255 and the sixth mirror current generating circuit 260 may beimplemented as a PMOS cascode current mirror circuit.

The fifth mirror current generating circuit 255 may include a pluralityof PMOS transistors P13 and P14 serially connected between a thirdmirror output terminal ND5 and the first power line through which thefirst power VDD is provided, and in a pull-up operation (or a currentsourcing operation), the fifth mirror current MI5 may flow to the thirdmirror output terminal ND5 through the fifth mirror current generatingcircuit 255.

The sixth mirror current generating circuit 260 may include a pluralityof PMOS transistors P15 and P16 serially connected between a fourthmirror output terminal ND6 and the first power line through which thefirst power VDD is provided, and in a pull-up operation (or a currentsourcing operation), the fifth mirror current MI5 may flow to the fourthmirror output terminal ND6 through the sixth mirror current generatingcircuit 260.

The second pull-up circuit PU2 and the fifth mirror current generatingcircuit 255 may configure a current mirror, and the second pull-upcircuit PU2 and the sixth mirror current generating circuit 260 mayconfigure a current mirror.

The amount of the third current 13 may be higher than the amount of eachof the fifth and sixth mirror currents MI5 and MI6, and the amount ofthe fifth mirror current MI5 may be the same as the amount of the sixthmirror current MI6.

For example, when it is assumed that lengths of channels of the PMOStransistors P11 to P16 are the same, widths of the channels of the PMOStransistors P11 and P12 are the same, widths of the channels of the PMOStransistors P13 to P16 are the same, and the width of the channel of thePMOS transistor P11 is K times the width of the channel of the PMOStransistor P13, the amount of each of the fifth and sixth mirrorcurrents MI15 and MI16 may be 1/K times the amount of the third current13.

Under such an assumption, when widths of the channels of the PMOStransistors P13 to P16 are capable of being adjusted by using controlsignals, the amount of each of the fifth and sixth mirror currents MI15and MI16 may be adjusted.

The fourth current mirror circuit 270 may be implemented as an NMOScascode current mirror circuit and may perform a mirroring operation onthe fourth current 14 to generate a seventh mirror current MI7 and aneighth mirror current MI8. Each of the seventh mirror current generatingcircuit 275 and the eighth mirror current generating circuit 280 may beimplemented as an NMOS cascode current mirror circuit. It may be assumedthat the fifth mirror current MI5 is the same as the seventh mirrorcurrent MI7 and the sixth mirror current MI6 is the same as the eighthmirror current MI8.

The seventh mirror current generating circuit 275 may include aplurality of NMOS transistors N13 and N14 serially connected between thethird mirror output terminal ND5 and the second power line through whichthe second power VSS, and in a pull-down operation (or a current sinkingoperation), the seventh mirror current MI17 may flow to the second powerline through the seventh mirror current generating circuit 275.Accordingly, a third output signal RX2L corresponding to a differencebetween the fifth mirror current MI5 and the seventh mirror current MI7may be output through the third mirror output terminal ND5.

The eighth mirror current generating circuit 280 may include a pluralityof NMOS transistors N15 and N16 serially connected between the fourthmirror output terminal ND6 and the second power line through which thesecond power VSS, and in a pull-down operation (or a current sinkingoperation), the eighth mirror current MI8 may flow to the second powerline through the eighth mirror current generating circuit 280.Accordingly, a fourth output signal RX2R corresponding to a differencebetween the sixth mirror current MI6 and the eighth mirror current MI8may be output through the fourth mirror output terminal ND6.

The second pull-down circuit PD2 and the seventh mirror currentgenerating circuit 275 may configure a current mirror, and the secondpull-down circuit PD2 and the eighth mirror current generating circuit280 may configure a current mirror.

The amount of the fourth current 14 may be higher than the amount ofeach of the seventh and eighth mirror currents MI7 and MI8, and theamount of the seventh mirror current MI7 may be the same as the amountof the eighth mirror current MI8.

For example, when it is assumed that lengths of channels of the NMOStransistors N11 to N16 are the same, widths of the channels of the NMOStransistors N11 and N12 are the same, widths of the channels of the NMOStransistors N13 to N16 are the same, and the width of the channel of theNMOS transistor N11 is K times the width of the channel of the NMOStransistor N13, the amount of each of the seventh and eighth mirrorcurrents MI7 and MI8 may be 1/K times the amount of the fourth current14.

Under such an assumption, when widths of the channels of the NMOStransistors N13 to N16 are capable of being adjusted by using controlsignals, the amount of each of seventh and eighth the mirror currentsMI7 and MI8 may be adjusted.

According to the above embodiment, the second output signal RX1Rgenerated by the first current mirror unit 130-1 and the third outputsignal RX2L generated by the second current mirror unit 130-2 are inputto the integrator 140-2 and thus, the integrator 140-2 performsdifferential operation on the second output signal RX1R and the thirdoutput signal RX2L.

As described above, since each of the output circuits 125-1 and 125-2and the current mirror units 130-1 and 130-2 is implemented as a cascodecurrent mirror, a direct current (DC) current mismatch of MOStransistors configuring each of the current mirror units 130-1 and 130-2may be minimized, and thus, a DC current accumulated into eachintegrator may be minimized. Accordingly, an output range of eachintegrator may be efficiently used, distortion of differential signalsmay be removed or considerably reduced, and a function of removingcommon noise caused by a mismatch with adjacent transmission channelsmay be enhanced.

In the above embodiments, it is described that the touch sensing deviceaccording to an embodiment of the present invention senses mutualcapacitance. However, the touch sensing device according to anembodiment of the present invention can be used to senseself-capacitance as illustrated in FIG. 4. Comparing the touch sensingdevice illustrated in FIG. 4 with the touch sensing device illustratedin FIG. 2, it is just different that the touch driving signal VDRV isdirectly input to noninverting terminal of buffers 120-1-120-n and theother elements and operations are same. Thus, the detailed descriptionabout the touch sensing device of FIG. 4 will be omitted.

FIG. 5 is a block diagram of a display apparatus including a touchsensing device and an in-phase/quadrature demodulator according toanother embodiment of the present invention. Referring to FIGS. 2 and 5,the touch sensing device 110A-2 of FIG. 5 further include a plurality ofreset switches SW1 and SW2 for respectively resetting feedbackcapacitors CF, a band pass filter 160, an I/Q demodulator 170, an Ichannel gain control and low pass filter 172, a first sample and holdcircuit 174, a Q channel gain control and low pass filter 182, a secondsample and hold circuit 184, a multiplexer 186, and an analog-to-digitalconverter 188, in addition to the elements 120-1, 120-2, 130-1, 130-2,140-2, and C_(F) of the touch sensing device 110A of FIG. 2.

Each of the reset switches SW1 and SW2 may respectively initialize thefeedback capacitors C_(F) in response to a reset signal RST.

The band pass filter 160 may receive the output signals V_(OUTP) andV_(OUTN) of the integrator 140-2, may perform band pass filtering on theoutput signals V_(OUTP) and V_(OUTN), and may output band-pass-filteredsignals to the I/Q demodulator 170.

The I/Q demodulator 170 may generate in-phase differential signals I andIB and quadrature differential signals Q and QB from theband-pass-filtered signals. Here, I may denote an in-phase component,and Q may denote a quadrature component.

The I channel gain control and low pass filter 172 may control a gain ofeach of the in-phase differential signals I and IB, may perform low passfiltering on gain-controlled in-phase differential signals, and mayoutput low-pass-filtered in-phase differential signals to the firstsample and hold circuit 174. The first sample and hold circuit 174 mayperform a sampling operation and a holding operation on thelow-pass-filtered in-phase differential signals.

The Q channel gain control and low pass filter 182 may control a gain ofeach of the quadrature differential signals Q and QB, may perform lowpass filtering on gain-controlled quadrature differential signals, andmay output low-pass-filtered quadrature differential signals to thesecond sample and hold circuit 184. The second sample and hold circuit184 may perform a sampling operation and a holding operation on thelow-pass-filtered quadrature differential signals.

The multiplexer 186 may provide output signals of the first sample andhold circuit 174 or output signals of the second sample and hold circuit184 to the analog-to-digital converter 188 in response to selectionsignals SEL. The analog-to-digital converter 188 may output outputsignals of the multiplexer 186 as T-bit digital signals. Here, T may bean integer of 2 or more.

Referring to FIGS. 2 and 5, it may be assumed in FIG. 5 that the touchscreen panel 103 is touched by an active pen PEN. A phase of a frequencyof a driving signal (for example, a sine wave or a square wave) for theactive pen PEN may be asynchronous with a phase of a frequency of thereference signal REF supplied to each of the buffers 120-1 and 120-2.Although the phase of the frequency of the driving signal for the activepen PEN is asynchronous with the phase of the frequency of the referencesignal REF supplied to each of the buffers 120-1 and 120-2, the touchsensing device 110A-2 including the elements illustrated in FIG. 5 maysense, by using the I/Q demodulator 170, that the active pen PEN touchesthe touch screen panel 103.

The elements included in the touch sensing devices 110A and 110A-2described above with reference to FIGS. 1 to 5 may configure a touchsensing circuit for sensing a touch applied to the touch screen panel103, and the touch sensing circuit may be implemented (or provided) inan analog front end (AFE).

According to the embodiments of the present invention, since a firststage is configured with a buffer and a current mirror unit and a secondstage is configured with a sensing amplifier for differentially sensingoutputs of current mirror units of adjacent channels, display noise andexternal noise occurring in common may be effectively removed.

Moreover, according to the embodiments of the present invention, sincethe buffers implemented in the touch sensing device are respectivelyconnected to the touch sensing lines of the touch screen panel, anadditional circuit (for example, a multiplexer) may not be neededbetween each of the buffers and a corresponding touch sensing line ofthe touch sensing lines.

Moreover, according to the embodiments of the present invention, sincethe buffers implemented in the touch sensing device are respectivelyconnected to the touch sensing lines of the touch screen panel, signalsmay be simultaneously generated or processed in all channels.Accordingly, comparing with a conventional time sequence manner where atouch sensing device sequentially senses signals of channels, anincrease in a sensing time may be reduced, and the degradation in signalquality caused by a time sequence-based sensing time difference may bereduced.

Moreover, according to the embodiments of the present invention, sincethe first stage is configured with buffers, a limitation of a feedbackfactor based on a high capacitance load may be reduced, and thus, it maybe easy to design a sensing amplifier and it may not be required toincrease a feedback capacitor, thereby minimizing an increase in adesign area and a reduction in an output signal of the sensingamplifier.

Moreover, according to the embodiments of the present invention, a gainof an output signal in the second stage may be adjusted by using acurrent mirror unit included in the first stage, and thus, a value of afeedback capacitor of a sensing amplifier included in the second stagemay be reduced, thereby maximizing the design area efficiency of thesensing amplifier.

Moreover, according to the embodiments of the present invention, areference signal for single-ended conversion may be selectively used ina first sensing amplifier and a last sensing amplifier, and thus, eachof differential signals may be converted into a single-ended signal byselectively using a channel, where noise or a touch does not occur, ofboth channels.

The above-described feature, structure, and effect of the presentdisclosure are included in at least one embodiment of the presentdisclosure, but are not limited to only one embodiment. Furthermore, thefeature, structure, and effect described in at least one embodiment ofthe present disclosure may be implemented through combination ormodification of other embodiments by those skilled in the art.Therefore, content associated with the combination and modificationshould be construed as being within the scope of the present disclosure.It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the disclosures. Thus, itis intended that the present disclosure covers the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A touch sensing device comprising: a plurality ofbuffers buffering a difference between a reference signal and areception signal received from a touch electrode through a touch sensingline and generating first and second currents corresponding to abuffered signal; a plurality of current mirror units respectivelyconnected to the plurality of buffers to generate a first output signalusing a first mirror current generated through mirroring of the firstcurrent and a third mirror current generated through mirroring of thesecond current and generate a second output signal using a second mirrorcurrent generated through mirroring of the first current and a fourthmirror current generated through mirroring of the second current; and aplurality of integrators integrating a difference between the firstoutput signal output from an n^(th) (where n is an integer of 2 or more)current mirror unit of the plurality of current mirror units and thesecond output signal output from an (n−1)^(th) current mirror unit ofthe plurality of current mirror units.
 2. The touch sensing device ofclaim 1, wherein each of the plurality of buffers comprises: anoperational amplifier including an inverting input terminal connected tothe touch sensing line to receive the reception signal, a noninvertinginput terminal receiving the reference signal, and an output terminalconnected to the inverting input terminal; and an output circuitincluding a pull-up circuit disposed between a first power line and theoutput terminal to allow the first current to flow and a pull-downcircuit disposed between a second power line and the output terminal toallow the second current to flow.
 3. The touch sensing device of claim2, wherein each of the pull-up circuit and the pull-down circuit is acircuit having cascode configuration including a plurality of MOStransistors serially connected to each other.
 4. The touch sensingdevice of claim 2, wherein the pull-up circuit is a PMOS cascode circuitincluding two PMOS transistors serially connected to each other, and thepull-down circuit is an NMOS cascode circuit including two NMOStransistors serially connected to each other.
 5. The touch sensingdevice of claim 1, wherein each of the plurality of current mirror unitscomprises: a first mirror current generating circuit disposed between afirst power line and a first mirror output terminal to generate thefirst mirror current by performing a mirroring operation on the firstcurrent; a second mirror current generating circuit disposed between thefirst power line and a second mirror output terminal to generate thesecond mirror current by performing a mirroring operation on the firstcurrent; a third mirror current generating circuit disposed between asecond power line and the first mirror output terminal to generate thethird mirror current by performing a mirroring operation on the secondcurrent; and a fourth mirror current generating circuit disposed betweenthe second power line and the second mirror output terminal to generatethe fourth mirror current by performing a mirroring operation on thesecond current, the first output signal is output through the firstmirror output terminal, and the second output signal is output throughthe second mirror output terminal.
 6. The touch sensing device of claim5, wherein each of the first to fourth mirror current generatingcircuits is a circuit having cascode configuration including a pluralityof MOS transistors serially connected to each other.
 7. The touchsensing device of claim 5, wherein each of the first and second mirrorcurrent generating circuits is a PMOS cascode circuit including two PMOStransistors serially connected to each other, and each of the third andfourth mirror current generating circuits is an NMOS cascode circuitincluding two NMOS transistors serially connected to each other.
 8. Thetouch sensing device of claim 1, wherein a first integrator of theplurality of integrators integrates a difference between a predeterminedreference signal and a first output signal output from a first currentmirror unit of the plurality of current mirror units, and a lastintegrator of the plurality of integrators integrates a differencebetween the predetermined reference signal and a second output signaloutput from a last current mirror unit of the plurality of currentmirror units.
 9. The touch sensing device of claim 1, wherein each ofthe first and second mirror currents is 1/K (where K is an integer of 2or more) times the first current, and each of the third and fourthmirror currents is 1/K times the second current.
 10. The touch sensingdevice of claim 1, further comprising: a band pass filter receiving andfiltering an output of a corresponding integrator of the plurality ofintegrators; and an I/Q demodulator demodulating an output signal of theband pass filter to generate an in-phase (I) signal and a quadrature (Q)signal.
 11. A touch sensing device comprising: a first buffer connectedto a first touch electrode through a first touch sensing line, the firstbuffer including a first output circuit including a first pull-upcircuit having a cascode configuration and a first pull-down circuithaving a cascode configuration; a first PMOS cascode mirror currentgenerating circuit connected to the first buffer to generate a firstmirror current by performing a mirroring operation on a first currentflowing through the first pull-up circuit; a first NMOS cascode mirrorcurrent generating circuit connected to the first buffer to generate athird mirror current by performing a mirroring operation on a secondcurrent flowing through the first pull-down circuit; and an integratorintegrating a difference between a predetermined reference signal and afirst output signal generated by using the first mirror current and thethird mirror current.
 12. The touch sensing device of claim 11, furthercomprising: a second buffer connected to a second touch electrodethrough a second touch sensing line, the second buffer including asecond output circuit including a second pull-up circuit having acascode configuration and a second pull-down circuit having a cascodeconfiguration; a second PMOS cascode mirror current generating circuitconnected to the second buffer to generate a second mirror current byperforming a mirroring operation on a first current flowing through thesecond pull-up circuit; and a second NMOS cascode mirror currentgenerating circuit connected to the second buffer to generate a fourthmirror current by performing a mirroring operation on a second currentflowing through the second pull-down circuit, wherein the integratorreceives a second output signal as the predetermined reference signal,the second output signal being generated by using the second mirrorcurrent and the fourth mirror current.
 13. The touch sensing device ofclaim 12, wherein each of the first and second mirror currents is 1/K(where K is an integer of 2 or more) times the first current, and eachof the third and fourth mirror currents is 1/K times the second current.14. The touch sensing device of claim 11, further comprising: a bandpass filter receiving and filtering an output of the integrators; and anI/Q demodulator demodulating an output signal of the band pass filter togenerate an in-phase (I) signal and a quadrature (Q) signal.
 15. Adisplay apparatus comprising: a touch screen panel including a pluralityof touch electrodes and a plurality of touch sensing lines connected tothe plurality of touch electrodes to each transmit a reception signalcorresponding to a capacitance generated in a corresponding touchelectrode; and a touch sensing device connected to the plurality oftouch sensing lines to sense whether a touch is applied thereto, whereinthe touch sensing device comprises: a first buffer connected to a firsttouch electrode through a first touch sensing line, the first bufferincluding a first output circuit including a first pull-up circuithaving a cascode configuration and a first pull-down circuit having acascode configuration; a first PMOS cascode mirror current generatingcircuit connected to the first buffer to generate a first mirror currentby performing a mirroring operation on a first current flowing throughthe first pull-up circuit; a first NMOS cascode mirror currentgenerating circuit connected to the first buffer to generate a thirdmirror current by performing a mirroring operation on a second currentflowing through the first pull-down circuit; and an integratorintegrating a difference between a predetermined reference signal and afirst output signal generated by using the first mirror current and thethird mirror current.
 16. The display apparatus of claim 15, wherein thetouch sensing device further comprises: a second buffer connected to asecond touch electrode through a second touch sensing line, the secondbuffer including a second output circuit including a second pull-upcircuit having a cascode configuration and a second pull-down circuithaving a cascode configuration; a second PMOS cascode mirror currentgenerating circuit connected to the second buffer to generate a secondmirror current by performing a mirroring operation on a first currentflowing through the second pull-up circuit; and a second NMOS cascodemirror current generating circuit connected to the second buffer togenerate a fourth mirror current by performing a mirroring operation ona second current flowing through the second pull-down circuit, whereinthe integrator receives a second output signal as the predeterminedreference signal, the second output signal being generated by using thesecond mirror current and the fourth mirror current.
 17. The displayapparatus of claim 16, wherein each of the first and second mirrorcurrents is 1/K (where K is an integer of 2 or more) times the firstcurrent, and each of the third and fourth mirror currents is 1/K timesthe second current.
 18. The display apparatus of claim 15, wherein thetouch sensing device further comprises: a band pass filter receiving andfiltering an output of the integrator; and an I/Q demodulatordemodulating an output signal of the band pass filter to generate anin-phase (I) signal and a quadrature (Q) signal.
 19. The displayapparatus of claim 15, wherein the touch sensing device furthercomprises a touch driving signal supply unit supplying a touch drivingsignal for driving the touch electrodes through the touch sensing lines20. The display apparatus of claim 15, wherein the touch screen panelfurther comprises a plurality of touch driving lines for supplying atouch driving signal, and wherein the touch sensing device furthercomprises a touch driving signal supply unit to generate and supply thetouch driving signal to the touch electrodes through the touch drivinglines.